One of the attractive features of block copolymers is the functionality which allows the creation of hybrid macromolecules composed of blocks that are normally immiscible with each other. These macromolecules often self-assemble to form many complex nanoscale morphologies that impart interesting properties and enable a wide range of applications. Macromolecular self-assembly using block copolymers is an active field in polymer research, wherein block copolymers self assemble to form nano-structured materials. One increasingly active application for these ordered structures is in the field of membrane technology.
Block copolymers are most commonly synthesized using special polymerization processes to produce polymers with very narrow polydispersity indices (PDI). While narrow polydispersity is normally desired in block copolymer synthetic protocols, broader polydispersity has a profound impact on phase behavior. Though a wide area of research has been directed at block copolymers, most research has been directed at macromolecular self-assembly utilizing block copolymers of monodisperse materials. Moreover, the capability to fabricate self-assembled structures for membranes with tailored domains has significant implications on scalability and applicability for this technology.
It is desirable that separation matrices are strong, thermally stable, and resistant to oxidative or corrosive elements. Such characteristics are often seen in hydrophobic polymers such as polysulfones or polyethersulfones. Polysulfones are widely used in ultrafiltration membranes for their chemical resistance, desirable mechanical properties, and good thermal stability. However, polysulfones are typically hydrophobic in nature. Hollow fiber and flat sheet ultrafiltration membranes comprising hydrophobic polysulfones are subject to poor wettability and fouling when used in separation and filtration applications.
Rather, a hydrophilic surface is desirable for use in the separation process of aqueous or polar materials. A hydrophilic or wettable surface on a porous polymer promotes uniform filtration and decreases adsorption of material such as protein and other solutes (e.g. fouling). Despite recent advances in the preparation of polysulfone compositions displaying enhanced hydrophilicity, further improvements and refinements in the performance characteristics of membranes comprising polysulfones are required. Thus, alternative separation matrices with both characteristics are needed to provide a broad spectrum of choices for purification of the many new products that are constantly being developed.
For production of therapeutic proteins, a system may contain several distinct filtration steps, including diafiltration, ultrafiltration, and viral clearance. The virus filtration step is an integral component of the bioprocessing stream for the reduction of endogenous virus particles or process-induced viral contamination. Next generation virus filtration membranes are expected to possess high virus log reduction, low fouling (e.g., material hydrophilicity), improved permeability, and robust material construction, which cannot be met by using currently available separation matrices.